Heretofore in drilling wells, including those in which the wellbore passes through a permafrost zone, water-based drilling fluids have been employed during the drilling procedure. These drilling fluids contain a major amount of water and therefore are freezable.
It is undesirable to leave freezable liquids in the permafrost part of a wellbore because, over the life of the well, the freezable liquid might be frozen and it is desirable that this be avoided.
Accordingly, it is desired to leave only essentially nonfreezable liquids in the wellbore in the area of the permafrost zone. It is just as desirable to continue drilling wells using water-based drilling mud. Therefore, it can be important to have a procedure for essentially completely displacing freezable liquid from portions of the wellbore. This can sometimes be difficult, particularly when the essentially nonfreezable liquid is lighter per unit volume than the water-based drilling mud because substantially complete displacement of a heavier liquid with a lighter liquid is difficult without using inordinate amounts of the lighter liquid.